The present invention relates to signal discriminator circuits and, more particularly, to an amplitude and rise time discriminator. In a specific embodiment disclosed herein, the discriminator is employed to detect the proper firing signal for detonation of a proximity fuze; however, it will be apparent to those in the art of electronic circuits that the scope of the present invention is not limited to fuze firing.
A major problem associated with proximity fuzes relates to premature firing which results in complete loss of the fired round. In addition, although premature firings cannot inflict casualties on friendly troops, they do constitute a psychological factor in the reluctance of troops to use proximity fuzes. It is therefore desirable to eliminate premature firing. A major cause of premature firing is spurious signals received at the fuze firing circuit. Such signals may result from enemy jamming operations or from within the fuze unit itself, such as by component failure, broken leads, or acoustic pick up.
There has been very little research conducted heretofore into the nature of the spurious signals which cause premature firings. I have discovered, however, that a substantial number of premature firings are initiated by burst-like spurious signals having an amplitude envelope with a significantly faster rate of rise than the amplitude envelope of the proper firing signal. Still other premature firings are initiated by signals with amplitude envelopes exhibiting a much slower rate of rise than the proper firing signal. More specifically, the proper firing signal is a sinusoidal signal which increases in amplitude at some predetermined exponential rate to a maximum amplitude. The spurious signals in question also increase to that maximum amplitude but at substantially faster or slower exponential rates than that exhibited by the proper firing signal. Since the proper and spurious signals achieve the same level, it is impossible to discriminate between them on the basis of amplitude alone. I have therefore devised a circuit which discriminates between signals on the basis of both amplitude and rate of amplitude rise.
It is therefore an object of the present invention to provide a circuit which is capable of discriminating between signals on the basis of both amplitude and rate of amplitude change.
It is another object of the present invention to provide a discriminator circuit for detecting signals reaching a predetermined amplitude and exhibiting a rate of amplitude rise lying within a predetermined range of rates.
It is another object of the present invention to provide an amplitude discriminator circuit which provides an output signal only when the amplitude rate of rise is slower than a first predetermined rate and faster than a second predetermined rate.
It is still another object of the present invention for providing a firing circuit for proximity fuze which discriminates against suprious signals and fires only in response to a firing signal of a least a predetermined amplitude and having a rate of amplitude rise within a predetermined range of rates.